JP2009036129A - Controller of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To sense accurately the change in the pilot injection amount caused by temporal change etc. without exerting an adverse influence to an exhaust gas. <P>SOLUTION: In the case where a sensing request is generated for a deviation from the target injection amount of the pilot injection amount (S1), the variable nozzle opening (VN opening) of a turbo supercharger is adjusted for dropping the suction pressure forcedly when the accelerator opening has decreased (S2), followed by changing over into an engine operating condition in which the degree of change in the main ignition delay to the change in the pilot injection amount is large (S3), and the main ignition delay is sensed (S4) and the actual pilot injection amount is calculated from the sensed main ignition delay (S5), whereupon the difference between the obtained actual pilot injection amount and the target injection amount calculated by an ECU is adopted as the deviation of the pilot injection amount due to the temporal change (S6). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control device for an internal combustion engine capable of fuel injection control in which main injection is performed after pilot injection, and more particularly to a technique for detecting a change in pilot injection amount with time.

  Conventionally, for example, for the purpose of reducing NOx, fuel injection control for performing main injection for generating output after pilot injection is known. In this case, the pilot injection is required to be accurately performed. However, the fuel injection amount of each device such as the fuel injection valve in the fuel injection device is changed by the change over time, and the fuel injection amount injected from the fuel injection valve. May change. For this reason, as disclosed in Patent Document 1, a technique for detecting a change with time of the pilot injection amount has been proposed.

According to Patent Document 1, the operation state is adjusted so that the main injection is difficult to be ignited due to the disappearance of the pilot injection. When a misfired cylinder is detected, the pilot injection amount is gradually increased until the misfire of the cylinder is eliminated, thereby changing over time. The amount of deviation of the pilot injection amount from the target injection amount is detected.
JP 2006-83719 A

  However, in Patent Document 1, since it is a condition that the combustion in the combustion chamber misfires when detecting the change with time of the pilot injection amount, there is a possibility that the exhaust gas may be adversely affected.

  The present invention has been made paying attention to the above problems, and an object of the present invention is to provide a control device for an internal combustion engine that can accurately detect a change in pilot injection amount due to a change over time without adversely affecting exhaust gas. And

  For this reason, the control device for an internal combustion engine according to the present invention detects the amount of deviation of the pilot injection amount from the target injection amount in an internal combustion engine capable of fuel injection control in which main injection is performed after pilot injection. The shift amount is detected based on the combustion state after switching to an engine operation state in which the degree of change in the combustion state with respect to the change in the injection amount is large.

  According to the present invention, since the amount of deviation of the pilot injection amount from the target injection amount is detected based on the combustion state without misfiring, adverse effects on the exhaust can be suppressed. In addition, since the amount of deviation of the pilot injection amount from the target injection amount is detected after switching to the engine operating state where the degree of change of the combustion state with respect to the change of the pilot injection amount is large, the sensitivity of the combustion state to the change of the pilot injection amount is detected. The detection accuracy of the amount of deviation can be increased.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a system configuration diagram of a diesel engine as a vehicle internal combustion engine to which an embodiment of a control device for an internal combustion engine of the present invention is applied.

  In FIG. 1, an intake compressor 3 a of a turbocharger 3 is disposed upstream of an intake passage 2 of the engine 1. The intake air is supercharged by the intake compressor 3a, cooled by an intercooler 4, passes through an electronically controlled intake throttle valve 5 driven by an actuator (not shown), and then passes through an intake manifold 6 to each of the intake air. It flows into the combustion chamber of the cylinder. The fuel is pressurized by the fuel injection pump 7 and sent to the common rail 8, and is directly injected into the combustion chamber from the fuel injection valve 9 provided for each cylinder. The air flowing into the combustion chamber and the injected fuel are combusted by compression ignition here, and the exhaust gas flows out to the exhaust passage 11 through the exhaust manifold 10. The fuel injection pump 7, the common rail 8, and the fuel injection valve 9 constitute a common rail fuel injection device.

  A part of the exhaust gas flowing out to the exhaust manifold 10 is recirculated to the intake manifold 6 from the EGR passage 12 via the EGR valve 13 as EGR gas. The remainder of the exhaust passes through the exhaust turbine 3b of the turbocharger 3 and drives it. The turbocharger 3 is a variable capacity turbocharger in which a variable nozzle driven by the actuator 14 is provided at the scroll inlet of the exhaust turbine 3b. The engine control unit 20 (hereinafter referred to as ECU 20) is used to connect the actuator 14 to the turbocharger 3. A predetermined supercharging pressure can be obtained by controlling the opening of the variable nozzle by driving control.

  In order to control the engine 1, the ECU 20 includes a crank angle sensor 21 that detects an engine speed and a crank angle, an accelerator opening sensor 22 that detects an accelerator opening, a water temperature sensor 23 that detects an engine cooling water temperature, and a cylinder temperature sensor. Signals are input from the in-cylinder pressure sensor 24 for detecting the in-cylinder pressure and the intake pressure sensor 25 for detecting the intake pressure.

  Based on these input signals, the ECU 20 performs a fuel injection command signal to the fuel injection valve 9 for controlling the fuel injection amount and injection timing of the main injection by the fuel injection valve 9 and the pilot injection performed prior thereto, the intake air An opening command signal to the throttle valve 5, an opening command signal to the EGR valve 13, a variable nozzle opening command signal to the actuator 14 of the variable capacity turbocharger 3, and the like are output.

  Further, the ECU 20 performs pilot injection amount detection control as described later at predetermined intervals, for example, in order to detect a deviation amount of the actual injection amount with respect to the target injection amount in the pilot injection due to the temporal change of the fuel injection valve 9. In the pilot injection amount detection control, the shift amount of the combustion state with respect to the change of the pilot injection amount is switched to the engine operating state, and then the deviation amount of the pilot injection amount is detected based on the change of the combustion state. I have to.

  The pilot injection amount detection control will be described in detail below.

  FIG. 2 is a flowchart of pilot injection amount detection control executed by the ECU 20.

  In S1, it is determined whether or not a pilot injection amount determination flag Fp = 1, and it is determined whether or not a request for detecting a pilot injection amount has occurred. The determination flag Fp is set to Fp = 1 every predetermined interval. For example, the determination flag Fp is set to Fp = 1 every time the traveling distance of the vehicle reaches a predetermined distance. Here, if the determination is YES, it is determined that there is a request for detecting the pilot injection amount, and the process proceeds to S2.

  In S2, it is determined based on the signal from the accelerator opening sensor 22 whether the accelerator opening has decreased by a predetermined value or more. If the value has decreased by a predetermined value or more, the determination is YES and the process proceeds to S3.

In S3, for example, the actuator 14 is driven and controlled to control the variable nozzle opening (VN opening) of the turbocharger 3, and the intake pressure is reduced to reduce the in-cylinder pressure at the compression top dead center.
Switch to the engine operating state for pilot injection amount detection. This is because, in the time chart of FIG. 3, as shown by the solid line, the engine rotation speed and the intake pressure decrease with a time delay with respect to the decrease in the accelerator opening (corresponding to the fuel injection amount and torque). As shown by the broken line in FIG. 3, the VN opening is forcibly adjusted to forcibly reduce the intake pressure. As shown in FIG. 4, the ignition of main combustion, which will be described later, is one of the combustion parameters related to the combustion state with respect to the change in the pilot injection amount under the condition where the intake pressure is low compared with the condition where the intake pressure is high. The change in the delay (hereinafter referred to as main ignition delay) is large. Therefore, by forcibly reducing the intake pressure, switching to the engine operating state in which the degree of change in the combustion state with respect to the change in the pilot injection amount is large is performed. Thereby, the sensitivity of the combustion state with respect to the change of the pilot injection amount is increased, and the detection accuracy of the pilot injection amount based on the combustion state can be increased.

  In addition, the intake pressure forced lowering control may adjust the opening of the intake throttle valve 5 (ETC opening) instead of the VN opening, and use both the VN opening and the ETC opening together. It may be. Further, as a method of reducing the in-cylinder pressure at the compression top dead center, the compression ratio may be lowered instead of the intake pressure, or both the intake pressure and the compression ratio may be lowered.

  In S4, the combustion state after the engine operation state switching control is detected as a combustion parameter related to the combustion state based on the change in the main ignition delay. Specifically, for example, the start timing of main combustion (combustion start crank angle CAign) is detected based on signals from, for example, the in-cylinder pressure sensor 24 and the crank angle sensor 21, and the main ignition delay is detected. Instead of the in-cylinder pressure sensor 24, a vibration sensor may be used to detect the vibration of the engine 1.

  As a combustion parameter for detecting the combustion state, instead of the main ignition delay, the maximum heat generation rate (dq / dθ) max or the maximum heat generation rate crank angle CA (dq / dθ) max may be used. The combustion state may be detected using at least one of these combustion parameters including the main ignition delay. The heat generation rate can be calculated by a known method from the in-cylinder pressure detected by the in-cylinder pressure sensor 24 and the in-cylinder pressure during motoring (a known value obtained by measurement in advance) (for example, Japanese Patent Laid-Open No. 7-180645). Issue gazette).

  In S5, the actual pilot injection amount Qpreal injected from the fuel injection valve 9 into the combustion chamber is calculated by an injection command from the ECU 20. Specifically, in the graph showing the relationship between the pilot injection amount measured and stored in advance by experiments or the like as shown in FIG. 5 and the main ignition delay, the combustion start crank angle CAign (main ignition delay) detected in S4 is shown. The corresponding pilot injection amount is assumed to be the actual pilot injection amount Qpreal.

  The same applies when the heat generation rate maximum value (dq / dθ) max or the maximum heat generation rate crank angle CA (dq / dθ) max is used as the combustion parameter instead of the main ignition delay. 6 is a graph showing the relationship between the pilot injection amount and the maximum heat generation rate (dq / dθ) max as shown in FIG. 6, or the pilot injection amount and the maximum heat generation rate crank angle as shown in FIG. The actual pilot injection amount Qpreal may be obtained from a graph showing the relationship with CA (dq / dθ) max.

  In S6, the difference between the actual pilot injection amount Qpreal detected in S5 and the target pilot injection amount Qpo calculated by the ECU 20 in accordance with the engine operating state is calculated, and this calculation result is calculated as a deviation amount of the pilot injection amount due to a change with time. Remember as.

  In S7, the pilot injection amount determination flag Fp is set to Fp = 0, and the pilot injection amount detection control is ended.

  Thereafter, using the stored deviation amount as a correction value for the pilot injection amount, the pilot injection amount command value output to the fuel injection valve 9 is set to the correction value so that the actual pilot injection amount Qpreal matches the calculated target pilot injection amount Qpo. Based on the above, fuel injection control is performed.

  According to the configuration of the present embodiment, since the sensitivity of the combustion state with respect to the change of the pilot injection can be increased, the deviation amount of the pilot injection amount with respect to the target injection amount can be accurately detected. In addition, by performing pilot injection amount detection when the accelerator opening is reduced, torque fluctuation due to the injection amount detection control shift can be suppressed, torque shock can be reduced, and since the fuel injection amount is low, the effect on exhaust is reduced. It is possible to suppress the deterioration of exhaust.

  In the above-described embodiment, the engine operating state is switched by lowering the intake pressure. However, the in-cylinder temperature is forcibly lowered by, for example, lowering the intake air temperature to switch the engine operating state. It is good also as a structure.

System configuration diagram of a diesel engine to which an embodiment of the present invention is applied Flow chart of pilot injection amount detection control Time chart explaining engine operation state switching operation for pilot injection amount detection The figure which shows the relationship between the pilot injection quantity and the main ignition delay due to the difference in intake pressure Diagram showing the relationship between pilot injection amount and main ignition delay The figure which shows the relationship between pilot injection quantity and the maximum heat release rate The figure which shows the relationship between pilot injection quantity and the maximum heat release rate crank angle

Explanation of symbols

1 Engine 3 Turbocharger 5 Intake throttle valve 9 Fuel injection valve 14 Actuator 20 ECU
21 Crank angle sensor 22 Accelerator opening sensor 24 In-cylinder pressure sensor 25 Intake pressure sensor

Claims (7)

In an internal combustion engine capable of fuel injection control for performing main injection after pilot injection,
When detecting the amount of deviation of the pilot injection amount from the target injection amount, after switching to an engine operating state where the degree of change in the combustion state relative to the change in the pilot injection amount is large, the amount of deviation is determined based on the combustion state. A control device for an internal combustion engine, characterized by being configured to detect.   The control device for an internal combustion engine according to claim 1, wherein the switching to the engine operating state is performed by lowering at least one of an in-cylinder pressure and an in-cylinder temperature at the time of compression top dead center.   The control apparatus for an internal combustion engine according to claim 2, wherein the in-cylinder pressure is reduced by reducing at least one of a compression ratio and an intake pressure.   The control apparatus for an internal combustion engine according to claim 2, wherein the in-cylinder temperature is lowered by lowering an intake air temperature.   Select at least one of ignition delay of main injection, maximum heat generation rate and maximum heat generation rate crank angle as a combustion parameter related to the combustion state, and based on a change in the value of the selected combustion parameter, The control device for an internal combustion engine according to any one of claims 1 to 4, wherein a deviation amount of the pilot injection amount from a target injection amount is detected.   The control device for an internal combustion engine according to any one of claims 1 to 5, wherein the detection of the amount of deviation of the pilot injection amount from the target injection amount is executed under an operating condition that has a small influence on torque shock and exhaust.   The control apparatus for an internal combustion engine according to claim 6, wherein the operating condition is when the accelerator opening is decreased.

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